Description: As with other clams of family
Veneridae (a very large family called the Venus clams), this species has
a porcelain-type (chalky) shell, the umbo
is anterior
to the midline (and to the hinge)
but still closer to the center of the shell than to the anterior
end, the hinge has
3 cardinal
teeth in each valve
(photo), and a definite pallial
sinus is present (photo). Other characteristics
of family Veneridae include: 2 valves
more or less oval or heart shaped, similar in size, and at least 1/4 as
wide
as long,
valves
are not subdivided into sections by major grooves or differences in texture,
do not have winglike extensions near the umbo,
have two adductor
muscle scars of similar size (photo), have no
chondrophore,
pallial
line is continuous (photo), hinge
ligament is mostly or completely external (photo).
This species has many radial
ribs which may be more or less prominent than the concentric ridges.
The concentric ridges are most prominent in the anterior
half. The hinge
ligament is about 1/3 the length of the shell (photo).
The siphons are
fused all the way to the end and have black tips (photo).
The valves are whitish
inside without a purple stain (photo) and have a
row of very small teeth along the inside of the ventral
margin (photo). The pallial
sinus is deep and pointed (photo). The
shell is whitish, gray, yellowish, or brown with little periostracum
on the outside and may have zigzag brown markings or brown splotches.
It usually does not exceed 6 cm long, max 7 cm..

How to Distinguish from Similar Species:
Look especially for the fine teeth on the inside ventral
margin of the shell. Venerupis
philippinarum, the Manila clam or Japanese Littleneck, is longer
than it is high and its radial
ribs are usually more prominent than in this species. Its siphons
are not fused all the way to the tips, and the ventral
margin of the shell has no fine teeth. Saxidomus
gigantea, the butter clam, has only concentric sculpture and the
shell gapes slightly at the posterior end. Protothaca tenerrima
is uncommon in protected bays and in sandy mud. Its hinge
ligament is nearly half the shell length and it grows as large as 8
cm. The cockle Clinocardium
nuttallii is a similar shape and has similar color patterns but
it has strongly serrated ventral
margins to the shell and the radial
ribs are much stronger than in P. staminea.
Note: Mercenaria mercenaria,
an Atlantic species, looks and keys very similarly to Leukoma staminea
and is also commonly sold in supermarkets. They even have the fine
serrations on the inside of the ventral margin of the valves. These
Mercenaria
can be distinguished from Leukoma by the fact that Mercenaria
usually has few radial ridges on the outside of the shell while Leukoma
typically has well-developed ones.

Habitat: In stable sand, packed mud,
or gravel-clay mixtures in protected areas, usually buried less than 8
cm below the sediment. Sometimes found in gravelly sediments among
rocks on the open coast. Occasionally found in empty burrowing clam
holes subtidally on the outer coast; in that situation they have raised,
concentric lamellae on their shell.

Biology/Natural History: This common
clam is not a true cockle but is sometimes called a rock cockle because
it is similarly shaped and has (fainter) radial ribs like some cockles
(see Clinocardium
nuttallii). It is often harvested and sold for food, though
it is is susceptible to paralytic shellfish poisoning. Often contains
larval tapeworms in large numbers (which cannot infect humans but do infect
the bat stingray). In quiet places such as Hood Canal it often grows
so abundantly that shells are nearly touching one another. The species
cannot dig fast so is not found in unstable sand. Predators include
oyster drill snails such as the leafy hornmouth snail Ceratostoma
foliatum and moon snails such as Euspira
lewisii, Octopus such as Enteroctopus
dofleini, sea otter, and the crabs Metacarcinus
magister and Cancer
productus. Pacific staghorn sculpins nip the extended siphons.
Spawns during the summer in British Columbia and Alaska, and grows slowly
(to only 2.5 cm in 2nd year, or even more slowly in Alaska). May
hybridize with other species such as P. tenerrima and Venerupes
philippinarum. The annual growth lines in the shell are distinct.
May live 8-16 years.

Leukoma staminea has short siphons which are fused
all the way to the end. The tips are black. The dark wispy
material accumulating near the excurrent siphon in the individual to the
right is pseudofeces.